Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

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1. In actual air-conditioning applications for R-12 and R-22, and operating at a condenser temperature of 40° C and an evaporator temperature of 5° C, the heat rejection factor is about

5.12

1.25

2.15

2. Rating of a domestic refrigerator is of the order of

0.1 ton

10 tons

5 tons

40 tons

3. A certain refrigerating system has a normal operating suction pressure of 10 kg/cm gauge and condensing pressure of about 67 kg/cm. The refrigerant used is

Carbon dioxide

Brine

Ammonia

Freon

4. A thermostatic expansion valve in a refrigeration system

Is suitable only for constant load systems

None of the above

Ensures the evaporator completely filled with refrigerant of the load

Maintains different temperatures in evaporator in proportion to load

5. In a lithium bromide absorption refrigeration system

Lithium bromide is used as a refrigerant and water as an absorbent

Water is used as a refrigerant and lithium bromide as an absorbent

None of these

Ammonia is used as a refrigerant and lithium bromide as an absorbent

6. A human body feels comfortable when the heat produced by the metabolism of human body is equal to the

(A) Heat dissipated to the surroundings

(D) Difference of (A) and (B)

(B) Heat stored in the human body

7. Critical temperature is the temperature above which

Water will never evaporate

A gas will immediately liquefy

Water will evaporate

A gas will never liquefy

8. The C.O.P. of a refrigerator working on a reversed Carnot cycle is (where T₁ = Lowest absolute temperature, and T₂ = Highest absolute temperature)

(T₂ - T₁)/T₁

T₂/ (T₂ - T₁)

(T₁ - T₂)/T₁

T₁ / (T₂ - T₁)

9. For obtaining high COP, the pressure range of compressor should be

Optimum

High

Any value

Low

10. The capillary tube, as an expansion device, is used in

Room air conditioners

Water coolers

Domestic refrigerators

All of these

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11. The curved lines on a psychrometric chart indicates

Dew point temperature

Relative humidity

Dry bulb temperature

Wet bulb temperature

12. The general rule for rating refrigeration systems (excepting for CO₂ system) is to approximate following h.p. per ton of refrigeration

2 to 5 h.p. per ton of refrigeration

0.1 to 0.5 h.p. per ton of refrigeration

1 to 2 h.p. per ton of refrigeration

0.5 to 0.8 h.p. per ton of refrigeration

13. The vapour compression refrigerator employs the following cycle

Carnot

Reversed Rankine

Reversed Carnot

Rankine

14. The value of C.O.P in vapour compression cycle is usually

Equal to unity

Always less than unity

Any one of the above

Always more than unity

15. Mass flow ratio of NH₃ in comparison to Freon-12 for same refrigeration load and same temperature limits is of the order of

1: 9

1: 1

9: 1

1: 3

16. Cooling water is required for following equipment in ammonia absorption plant

Condenser, absorber and separator (rectifier)

Evaporator

Absorber

Condenser

17. In a flooded evaporator refrigerator, an accumulator at suction of compressor is used to

Superheat the vapour

Detect liquid in vapour

Collect vapours

Collect liquid refrigerant and prevent it from going to compressor

18. The atmospheric air at dry bulb temperature of 15°C enters a heating coil maintained at 40°C. The air leaves the heating coil at 25°C. The bypass factor of the heating coil is

0.67

0.376

0.4

0.6

19. In a refrigeration system, the expansion device is connected between the

Evaporator and compressor

Compressor and condenser

Receiver and evaporator

Condenser and receiver

20. Which of the following cycles uses air as the refrigerant?

Bell Coleman

Carnot

Stirling

Ericson

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21. The condition of refrigerant after passing through the condenser in a vapour compression system is

Dry saturated vapour

Wet vapour

Superheated vapour

Saturated liquid

22. The freezing point of sulphur dioxide is

-56.6°C

-77.7°C

-75.2°C

-135.8°C

23. Which of the following statement is correct?

(B) The increase in air movement increases the evaporation from the human body.

(D) Both (A) and (B)

(A) The human body can lose heat even if its temperature is less than the atmospheric temperature.

24. A bootstrap air cooling system has

Four heat exchangers

Three heat exchangers

Two heat exchangers

One heat exchanger

25. A reversible engine has ideal thermal efficiency of 30%. When it is used as a refrigerating machine with all other conditions unchanged, the coefficient of performance will be

2.33

4.33

3.33

1.33

26. Freon group of refrigerants are

Toxic

Inflammable

Non-inflammable and toxic

Nontoxic and non-inflammable

27. The change in evaporator temperature in a refrigeration cycle, as compared to change in condenser temperature, influences the value of C.O.P.

Less

Equally

Unpredictable

28. In a refrigeration system, heat absorbed in comparison to heat rejected is

More for small capacity and less for high capacity

Less

Same

29. When the temperature of the surrounding is higher than the temperature of the body, then the heat loss by convection from the body to the surrounding will be

Negative

None of these

Positive

Zero

30. On the pressure-enthalpy diagram, condensation and desuperheating is represented by a horizontal line because the process

Takes place at constant temperature

Takes place at constant entropy

Takes place at constant pressure

Involves no change in volume

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31. The minimum temperature to which water can be cooled in a cooling tower is

Ambient air temperature

Dry bulb temperature of air

Wet bulb temperature of air

Dew point temperature of air

32. Most thermostatic expansion valves are set for a superheat of

20°C

10°C

15°C

5°C

33. The bank of tubes at the back of domestic refrigerator is

Condenser tubes

Evaporator tubes

Capillary tubes

Refrigerant cooling tubes

34. The refrigerant after condensation process is cooled below the saturation temperature before throttling. Such a process is called

Super-cooling

None of these

Sub-cooling or under-cooling

Normal cooling

35. The operating pressure for refrigerating units using R-12 as a refrigerant is

30 bar

8 bar

15 bar

2 bar

36. The boiling point of ammonia is

-77.7°C

-30°C

-10.5°C

-33.3°C

37. If a heat pump cycle operates between the condenser temperature of +27°C and evaporator temperature of -23°C, then the Carnot COP will be

1.2

0.2

38. Which of the following is not a desirable property of a refrigerant?

High risibility with oil

Good electrical conductor

Large latent heat

Low boiling point

39. Highest temperature encountered in refrigeration cycle should be

Near critical temperature of refrigerant

At critical Temperature

Above critical temperature

Much below critical temperature

40. The domestic refrigerator uses following type of compressor

Axial

Piston type reciprocating

Centrifugal

Miniature sealed unit

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A Demrot is the founder of VideRime Online Learning, a leading engineering website. He did his BE Civil and M.Tech Structure from RGPV University, Bhopal and has been working as an Assistant Professor in a reputed college.

Refrigeration & Air-Conditioning Practice Set-3

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